This invention relates to microwave switches and, more particularly, to a high isolation fast state transitioning switch using balanced configurations and switch drivers.
Traditional microwave switches are provided in microstrip (MS) technology or coplanar waveguide (CPW) technology. Certain devices are also used for microwave switches such as the PIN diode, the Schottky diode, and the IMPATT diode, for example. Such diodes are high power switches, however, in many applications high switching speeds are not required. In simplest terms, the most desirable switch would be one that was a short circuit for a first bias condition or closed position, and an open circuit for a reverse bias condition. However, in practice, significant problems arise with microwave switches. In the microstrip or coplanar waveguide technology, the isolation is not as good as desired because the inputs or lines to be switched are not balanced. In the case of coplanar waveguides and microstrips, the input signal and the return signal are not close to one another and therefore there is a great deal of interference and spurious propagation due to radiation effects, resulting in poor isolation between input and output signals.
For high frequency applications (e.g. at millimeter wavelengths), it becomes extremely difficult to implement lumped component based switches that have a switching speed of about 100 picoseconds (pS) with greater than about 25 dB of isolation. One solution involves the use of SRD diodes with Schottky diodes. Basically, a Schottky diode is formed by a deposition of a metal contact on a semiconductor crystal. The Schottky junction diode is a majority carrier device. This implies that there is only a very small stored charge in the junction of the diode as compared with a p-n junction that is a minority carrier device. The SRD diode also performs switching in conjunction with Schottky junctions. These devices are difficult to implement and to provide consistent operation in large scale, large quantity operations. They involve adjustment of many parameters after fabrication to control the switching time. Furthermore, the operating characteristics are inconsistent from device to device and batch to batch. Still further, requirements such as driver switch combinations operative with 100 picosecond (pS) rise time pulses make manufacturing and implementation using the above-identified devices difficult if not impossible.
It is therefore desirable to provide a microwave switch which is capable of high-speed operation and would be further compatible with modern integrated circuit techniques.
A high speed switching apparatus comprises first and second parallel balanced lines each directed from an input line end to an output line end and spaced apart one from the other and adapted to receive equal and opposite currents to provide balanced operation. Third and fourth parallel balanced lines are spaced apart one from the other and each directed from an input line end to an output line end and adapted to receive equal and opposite currents to provide balanced operation, wherein the input end of the third and fourth lines are separated from the output end of the first and second lines. A first switch is coupled between the output end of the first line and the input end of the third line, and the switch is operative in a first high impedance off state and a second low impedance on state. A second switch is coupled between the output end of said second line and the input end of the fourth line, and the switch is operative in a first high impedance off state and a second low impedance on state. A switch driver is coupled to the first and second switches to operate the switches in the off or on state according to a control signal applied to the driver, whereby when the driver operates the switches in the on state any signal propagating on the first and second lines propagates on the third and fourth lines and when the driver operates the switches in the off state any signal propagating on the first and second lines does not propagate on the third and fourth lines. The first, second, third and fourth lines are each metalized conductive lines located on a semiconductor substrate. In addition, each of the lines has an inductive reactance coupled thereto with a portion of the reactance associated with each line located on a top surface of the substrate, and another portion on a bottom surface of the substrate to provide symmetrical, equal reactive components for each of the lines.
An integrated balanced line microwave switch configuration comprising an input balanced line configuration coupled to an output balanced line configuration via a pair of switching transistors, the switching transistors controlled between a conductive on-state and a non-conductive off-state by means of a switch driver, the switch driver operative with the balanced line configurations to control the transistors between the conductive on-state where the input balanced line configuration is electrically coupled to the output balanced line configuration, thereby enabling a signal to propagate from the input balanced line configuration through the switching transistors to the output line configuration, and the non-conductive off-state where the input balanced line configuration is electrically isolated from the output balanced line configuration, thereby prohibiting a signal to propagate from the input balanced line configuration through the switching transistors to the output line configuration.